Method and means for relaying modulated carrier waves



P. WOLD. METHOD AND MEANS FOR RELAYING MODULATED CARRIER WAVES.

APPLICATION FILED FEB, I7. I9]?- Patented Aug. 8, 1922.

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PETEE I. 'WQLD, @15 EAST @RANGE, NEW J'E'JEfiEY, ASSZGNQR T ELEQTRSZQ @QEEPANY, KNCGEPOFJATED, @F NEW 'YQB Z, It. 351, it. CQRPGJRATIQN @IE NEVL YG IELK.

HETEGD AND EEEAEQS RELATING IiODULATED Specification of Letters Patent. Pafi gn'tgd 111mg, 3, 15322,

Application filed February it, 1917. tierlal Ito. 149,213.

T 0 all whom it may concern.

Be it known that l, it. Wow, a citizen of the United States, residing at East @range, in the county of Essex and State of New Jersey, have invented certain new and useful Improvements in Methods and Means for helaying Modulated Carrier l laves, of which the following is a full, clear, concise and exact description.

This invention relates to systems torrelaying or repeating such signals or other low frequency impulses as are carried by high frequency oscillations of the type used in radio transmission.

In particular it embodies a system in which high frequency oscillations, modulated in accordance with low frequency sig nals, are received at an intermediate or relay station and are so changed in character that there is no tendency to produce singing. This object is attained by receiving, at the relay or repeating station, the modulated high frequency oscillations and impressing them on a suitable device, such as a thermionic vacuum tube modulator. The

output circuit of such a modulator will contain a certain number of oscillations of high and of low frequency, one at least of which consists of a carrier wave of double the original carrier frequencyand modulated in ac cordance with the original signal. This component of the output may be selected out by suitable circuits and, after amplification, may be transmitted to a remote station. This modulated doubled frequency will have little or no efiect upon the receiving antenna at the repeating station for the receiving system is tuned to the original carrier frequency. Thus the tendency to sing. which is so common in all relay systems is eliminated.

In British Patent 142,371, it is shown how singing at a wireless repeating station may be avoided by combining thev modulated waves received at a repeating station with locally generated oscillations of another high frequency, whereby modulated oscillotions are'produced having a'carrier frequen'cy different from the carrier frequency received. Modulatel oscillations of the new carrier frequency are transmitted from the repeating station to a distant station, the

recelvmg apparatus at the repeating station being unresponsive to-the new carrier frequency.

If the local generator at the repeating station does not keep in step with thegenerator at the sending station, beats will be produced having a frequency equal to the difference in the frequencies of the generators. The heats are objectionable as they mask the signal to be received.

The present invention relates to improvements in the above system, in that the local generator at the repeating station is dispensed with and the carrier frequency is changed by impressing the received modulated wave upon an audion tube or a similar 7 device having a curved input-voltage, output-current characteristic, and which functions as does a modulator to produce sum and difference frequencies. in the ordinary method of modulation, when the carrier frequency p is modulated by the low frequency a, there are produced the sum and difference frequencies p+a and p-e, termed in the art, side frequencies which, with the carrier frequency 3?, go to make up the ordinary modulated wave According to the present invention, the three components, p, p+(t, and pa are combined in a modulator to produce in a similar manner the sum frequencies p+(p+0:}: :Zp-l-a. and p+ (pct:2pa, and {p+a)+ (yr-a) :27). These three components 2p, 2p+a, and Qp-a represent a carrier wave of frequency of 2p, modulated by the low,

frequency 4;. These components may be selected from the various frequencies supplied by the modulator, amplified and transmitted to a distant station, without afiecting the local receiving apparatus which is responsive to the modulated carrier frequency p and not to the modulated carrier frequency 2;). A local circulation of power or singing at the repeating station is accordingly.

Edd

reference letter of carrier currents 1 which are modulated in any suitable manner by the signals impressed on the signaling device 2. As shown herein the signaling currents in the'circuit 3 and the carrier currents'from source 1 are impressed on the input circuit 4: of the vacuum tube modulator 5 of the audion type. The grid 22 of modulator 5 is maintained at a negative potential by battery 23 andspace current in the modulator output circuit is supplied by battery 24. The carrier currents are variably amplified in accordancewith the comparative y slowly varying potential which the signaling currents assign to the grid 22. This modulating system is described and claimed in United States Patent 1,350,752 to H. J. Van der Bijl, high frequency signaling, patented August 24, 1920.

The modulator M supplies a modulated wave of usual form having the components p, p+ai, p-a. To improve the quality ofthe speech received at station Z, as later described in detail, one of the side frequencies p+a or p-a is suppressed, for instance, by

-means of-the filter F of the well-known cuit of modulator Campbell type, cou led to the output cir- M by means of the transformer 25. The unsuppressed components, having frequencies 1) and p+a or p and p-a,

. depending upon whether p-a or p-l-w has nsuppressed, may be amplified by means of one or more amplifiers 26 similar to amplifiers 15 at station Y. The unsuppressed components, after amplification, are sent to the antenna 7 by means of the transformer 6. The modulated wave having either the components 1) and p+a,'or p and 72-11, is

transmitted from station X and received by the antenna 8 at receiving station Y. Coupled to the antenna 8 by means of the transformer 9 is the amplifier 10, the input circuit of which is tuned flatly to the mean of the frequenciesto be received. The output circuit of the amplifier 10 and the input circuit of the modulator 11 are'tuned by means ectively, to the modified modulated wave to e transmitted. The output circuit of the modulator 11, which is a vacuum tube of the audion type, is tuned by meansof the condenser 14 to transmit the frequencies 2;) and 2p-I-a, currents of these fr ue'ncies being amplified by the bank of amp ifiers 15,.t he input circuit of which is tuned by means of the condenser 16 to the frequencies 2p and 2p+a,

and the output circuit of which delivers the "amplified components 2p and 2p+a to the antenna 17. Thusby combining the ener of the incoming modulated waves will energy of different characteristic, such for example as that supplied by the space current sources of thevacuum tubes, modulated waves of a carrier frequency twice that of the incoming waves are produced. Modified modulated currents of the doublecarrier frequency are transmitted to the antenna 18 at the receiving station Z. Any suitable means may be provided at this station for receiving the signal. For instance, the recomponents 2, p i-a, pa, the-n'currents of the following frequencies will be received in the output circuit of modulator 11,219, 212+i1, 2p-a, 2p+2a, 2p2w. The detector 19 acts as does the modulator 11 to produce the sum and difference frequencies, so that the above frequencies, when transmitted from station Y and received at station Z, where they are impressed on the input circuit of detector 19, produce in the output circuit of this detector the following high frequencies: 4p, pia, 4pi2a, 4pi3a, 4121405, which are inaudible, and the signal frequencies 1, 2a, 3a, and 4a. The frequencies 2a, 3a, 4a are overtones of the fundamental frequency a and the received signal wave form of frequency a will be distorted because of these overtones.

It is desirable to prevent the overtones from masking or distorting the receiving signal and to this end the invention -pg'ovides, preferably at the sending station the filter .F to suppress one of the side frequencies, either the frequency p+a or 12- a, so that there is transmitted from station X either the frequencies p and 12-0, or p and gH-a. In case a modulating system of the type shown isused at station X, then, preferably the filter is located between the modulator :5 and the amplifiers 26 so that the amplifiers need handle only the frequencies to be radiated. It is obvious, however, that the filter F may where in the sending and receiving system in advance of the modulator 11. When the filter F is used and the modulator 11 is supgilied with onl the frequencies p, and p-l-a, or example, t e output circuit the modulator will contain frequencies: 2p, 2p+a', 2p+2a. These frequencies on being received at station Z will to receive the fre-' be located any-v the following produce in the output circuit of the detector Y 19 the following high uencies: 4p, 4p+a,

and only the signal frequencies a and 2a, and

incense is found to be large. When-both side frequencies are freely transmitted, as first assumed, the amplitude of frequency a as compared to that of 2a is less than when the filter is used, while the amplitude of the component a as compared to the sum of the components 2a, 30: and do is still less. The advantage of using the filter is apparent as the overtones 3a and do are practically entirely suppressed, amplitude of 2a to a is reduced.

In addition to the above described reduction in amplitude of the overtone 2a, a further reduction may be secured by making the amplitude of the frequency 39 large as compared to the amplitude of the side frequency transmitted, n+0; for example, as above assumed. This may be done by trans: mitting from the sending station, a large amount of unmodulated carrier currents. ll the amplitude of p is large as compared to that of p+a, then in the output circuit of modulator 11, the amplitude of 2p and Qgo+a will be large as compared to the amplitude of the frequency 2p+2a which is the first overt/one oil the weak fundamental frequency ga-l-a. It follows that, in the output circuit of detector 19, the amplitude of the audible frequency a, will be large as compared to that of 2a, since the amplitude of 0: depends on the combination of the fregquencies Qp and 2p+a, both of which are strong, while the amplitude of the frequency 20. depends on the combination of 2p and 2p+2a, the latter 2p-l-2a being comparatively weak in amplitude.

Asthe modulated wave transmitted from the antenna 17 at the station Y has the carrier frequency 2;), to which the antenna. 8 at station Y is unresponsive, a local circulation of power or singing at. the station Y is prevented.

While the invention has been described in connection with a radio telephonic. signaling system, it is obviously equally applicable to either wire or radio systems in which signals of any form, control impulses for distant mechanism, 'or other transmitted energy ap pears in one stage of transmission as varyin or interrupted electrical current.

at is claimed is:

1. The method of repeating electrical impulses which consists in receiving from a distant station carrier waves modulated in accordance with said electrical impulses, controlling local energy by said received waves to produce similarly modulated waves having a carrier frequency which is diilerent from that of said received waves and which is determined solely by the received waves and independently of any characteristic of said local energy, and transmitting said modulated difierent frequency carrier waves to a. remote point.

2. The method of repeating electrical imand the comparative pulses which consists in receivin from a distant station carrler waves mo ulated in accordance with said electrical impulses, confrom that of said received waves and which is determined solely by the received waves and independently of any characteristic of said local energy, and amplifying and transmitting said modulated different frequency carrier waves.

3. The method of transmission by means of carrier waves modulated in accordance with electrical impulses which consists in transmitting substantially exclusively cur rents of the carrier "frequency and currents of one side frequency.

The method which comprises producing a complex wave having components of the carrier frequency 20 and the side fre quencies p-l-a and p-a differing from the frequency p by the signal frequency a, and in suppressing one oi said side frequency components.

5. lln a repeating system, the combination of a high frequency line adapted to receive a signal modified carrier wave from a distant station, a local source of energy, means for controlling said local energy hy said received wave to produce a resulting similarly modified carrier wave having a carrier frequency difiering from that of the received wave and which is determined solely by said received wave independently of any characteristic of said local energy, and means for transmitting said resulting difilerent frequency carrier wave.

6. A repeating system comprising a high frequency line adapted to receive a signal modified carrier wave from a distant station, means for deriving from said received carrier wave a second carrier wave similarly modified and having a carrier frequency which is a multiple of that of said received wave and which is determined solely by said received wave independently of any local agency, and means for selecting said multip e frequency carrier wave for transmission.

7. A repeating system comprising a high frequency line adapted to receive from a dlstant station a carrier wave modulated in Milli lllll llllll) accordance with signals, means for control- V means for transmitting said modulated.

frequency to a dis-v wave of doubled carrier taut station.

The method ofrepeatingsials which we comprises receiving carrier waves modulated in accordance with said signals and controlling by the energy of said modulated carrier waves energy of different characteristic to produce modulated waves having a carrier frequency twice that of said received modulated waves, and which carrier fre-' quency is determined solely by said received carrier Waves independently of any quality of said energy of diiferent characteristic.

9. lhe method of radio transmission which comprises causing the energy of received carrier waves modulated in accordance with impulses of lower frequency to control energy from a local source to produce similarly modulated carrier waves having a carrier frequency twice that of said received modulated waves, and which carrier frequency is determined solely by said received carrier waves independently of any characteristic of the energy of said local source.

10. The method which comprises modulating a carrier wave, suppressing one of the components of the modulated wave, and distorting the waveform of the resulting energy by combining its components to produce a second carrier wave of difi'erent frequency modulated in the same manner as the first mentioned carrier wave.

11. A transmission system comprising means for producing a carrier wave, means for modulating said wave, means for suppressing one of the components of the modulated wave, and means for distorting the Wave form of the resulting energy by com-- bining its components to produce a second carrier wave of different frequency mod-' ulated in the same manner as the first mentioned carrier wave.

In witness whereof, I hereunto subscribe my name this 16th day 021: February A. D.,

PETER I. WOLD. 

